The objective of the research project is to provide insight into the mechanism of exocytosis in epithelial cells, especially to identify components in the fusion partners, secretion granule and apical plasma membrane, which could contribute to their specific interaction. Secretion granules, their limiting membranes, and plasma membranes have been obtained as purified fractions (by centrifugation) from homogenates of rat parotid salivary gland. Both membrane fractions are enriched in Gamma-glutamyl transpeptidase (GGTP) activity while only the plasma membrane fraction exhibits potassium-stimulated p-nitrophenyl phosphatase (K+-PNPP ase) activity. Most plasmalemmal fragments contain morphologically recognizable apical and lateral domains separated by elements of the junctional complex; consequently, we will examine the topographic distribution of K+-PNPP ase (by histochemical techniques) and GGTP as well as other granule-associated polypeptides (by immunocytochemical techniques using antibodies raised against GGTP purified from rat kidney and against purified granule membranes). Information obtained will be used to guide attempts to separate plasmalemmal subfractions enriched in apical and lateral domains, respectively. Comparative compositional analysis of granule membrane and plasmalemmal subfractions will orient future investigations of macromolecules identified as potential participants in the specific recognition and membrane rearrangement processes of exocytosis. Further, comprehensive characterization of the functonal role of GGTP in these membranes may aid in defining conditions which prevail in luminal spaces of exocrine glands where massive quantities of secretory protein disaggregate and are conveyed to their sites of action. Thus, the proposed research may provide insight into possible mechanisms by which exocrine secretions attain high viscosities and inhibitory capacities for ion resorption in cystic fibrosis.